OCN 201 LAB FALL 2003 POLYNESIAN AND WESTERN NAVIGATION

Transcription

1 Name: OCN 201 LAB FALL 2003 POLYNESIAN AND WESTERN NAVIGATION INTRODUCTION People have been sailing the seas for thousands of years, during most of which time they relied on the sun and the stars to navigate the open ocean. It wasn't until the invention of the compass and the clock, along with other advances in the fields of geophysics and astronomy, that extremely accurate navigational techniques were utilized. This lab will provide an overview of both Polynesian and modern wayfinding. You will use computer simulation, a star compass, a magnetic compass, and a GPS unit to learn more about wayfinding techniques. During this lab you should accomplish the following objectives: 1. Use maps to identify Latitude and Longitude, magnetic and true north; 2. Find the coordinates of Oahu; and 3. Learn orientation skills based on a star chart and a compass. If you need further clarification after reading the sections below, please read Appendix 3 of the class textbook, Oceanography: An Invitation to Marine Science by Tom Garrison. POLYNESIAN NAVIGATION The required reading for this section is found on the Polynesian Voyaging Society (PVS) web site at Click on the Wayfinding link and then the Wayfinding Summary link. Interested students should review the rest of the site to learn more about PVS and traditional wayfinding techniques. MODERN NAVIGATION Instead of splitting the sky into star houses, modern navigators split the globe a system of quadrants formed by imaginary lines called latitude and longitude. Latitude lines run parallel to the equator and indicate North or South positions. Longitude lines run from pole to pole and indicate positions on meridians East and West of the Greenwich meridian (designated as the zero meridian). By convention, degrees (symbol o ) and minutes (symbol ) are the units used to describe position. This is based on 360 o in a circle and 60' in a degree. When writing coordinates, the latitude always goes first. For example, the coordinate "22 o 18.5 N 155 o 34.6 W" is read as "22 degrees, 18.5 minutes North and 155 degrees, 34.6 minutes West." The distance between each line of latitude is the same and one degree of latitude is equal to 60 nautical miles (1 nautical mile = 1.15 mile). In contrast, lines of longitude are not spaced evenly. At the poles, all lines of longitude converge. At the equator, lines of longitude have their greatest spacing, which is equal to the distance between lines of latitude. For the purposes of this lab, we will assume that one degree of longitude is equal to 60 nautical miles because Hawai'i is reasonably close to the equator. To find out location relative to the latitude/longitude coordinate system, modern navigators use equipment such as charts (nautical maps), a magnetic compass, and the Global Positioning System (GPS). The basis for the magnetic compass is discussed below, followed by a brief discussion of GPS.

2 The earth's magnetic field is probably caused by motions in the liquid outer core. This magnetic field has been moving around over the history of the earth, but also the poles have been flipping sides! They also drift to a small extent. Figure 1 illustrates the movement of the North magnetic pole over the past 100 years. Right now, it seems to be 8 degrees south of the geographic North Pole. This means that depending on where you are in the world, you have to be careful to correct the reading on your compass accordingly. Figure 1: The position of the magnetic North over time. As you can see, the magnetic North in the year 2000 was on 250 o in this strange projection. That is the same as 110 o West in the system we are familiar with. Figure courtesy of USGS: The difference between the magnetic and the geographic North Pole is referred to as the declination. The declination of a map changes from year to year, so if you use an old map, you will end up travelling off course. For this laboratory, we read on our map that if we are in the Hawai`ian Islands, the magnetic North lies 10 degrees east of the geographic North, as we look towards it. That means that we must subtract 10 degrees from our compass reading to see our direction in relation to the geographic North. This direction in relation to the geographic North is known as the bearing. For example, if our compass says that we are looking in a direction of 275 o, our bearing is 265 o. 2

3 GPS uses satellites that are orbiting the earth to transmit signals to a receiver on earth. Multiple satellites transmit signals to a single receiver. By analyzing the distances between you and each of the satellites, your GPS unit determines your location. This method is referred to as triangulation and your TA will explain it further during lab. EXERCISES I. Basic Navigation Tools The TA will bring groups of students onto the roof of MSB or out into the courtyard in front of the building and demonstrate the GPS and compass. 1. What are the latitude and longitude of UH Manoa? Lat Long 2. By walking with the GPS unit turned on estimate (using your stride to measure) what is the minimum distance that you need to walk to cause the GPS display to change by its minimum value? 3. From the assigned point outside the building or on the roof, what is the bearing of a) POST, b) HIG, c) Bilger Hall? II. Modern Navigation Methods 4. Using the assigned worksheet and the chart of the main Hawaiian Islands, draw a course on the chart using the erasable marker. For this exercise, refer to the table below. You will begin by determining the coordinates (position) of Hanauma Bay. Then, go 60 nautical miles at a bearing of 140 and write down your location and position in part B. For the position, give your coordinates to the nearest minute. For the location, write down the closest land- or sea-mark. If you are in the middle of a channel, which one? If you're right next to a point or cape, which one? You get the idea 3

4 Location Position Bearing Distance A. Hanauma Bay nautical miles B n miles C n miles D n miles E. You should now be at 21 N, 159 W. If that's where you ended up, good work! If not, you can recheck your route to see where you've made mistakes. Now, plot the bearing and distance to Nawiliwili Bay, Kau'ai. Put your answer in the space below. III. Polynesian Navigation Methods 5. Using the marked Hawaiian star compass rose (provided to you in class), give the direction for each of the bearings used above. Note that these legs correspond with the voyage that you plotted in the previous exercise. Also, calculate how much time would be spent on each leg of the journey if you were travelling at 15 knots (1 knot = 1 nautical mile per hour). Round to the nearest 1/4 hour. Note that this is a rather impossible speed if travelling on a vessel such as the Hokule'a when sailing in a multitude of directions, but we will use it anyhow. Degrees Hawai'ian Direction Name Distance (n miles) Time (hours) A nautical miles B nautical miles C nautical miles D nautical miles E. 4

5 6. Use the computer program "Starry Night Backyard" to identify the stars that can be used to hold the canoe's course during the above journey. Basic instructions for using Starry Night Backyard: 1) Open the program by clicking on the astronomical observatory icon on the launching dock. 2) Take a few minutes looking at the program, the menus and the clickable buttons. 3) At the top of the window with the view of the meadow you can see the following, from left to right: The date and time. You can change these by clicking on them and typing in the numbers. Speed with which time moves. You can speed time up 30 times, 300 times etc. VCR-like controls that can stop time, move time forwards or backwards etc. Elevation and location 4) Look at the menu on the left of the screen: Select View Options. To have the program label planets, stars and constellations, check the boxes marked Labels next to these items. 5) Place the computer mouse over the landscape, hold down the mouse button and move the mouse left or right. This way you can look around you in any direction you wish. 6a. Look at the menu on the top of the screen. Select View, and scroll down to Hide Daylight. Now you can see the stars and constellations obscured by daylight. Set the speed with which time moves at 3000x. Look in different directions and describe the motion of the stars as you face each direction. South East North West 6b. When facing the north, which star doesn t move? How could this star be useful in determining your bearing? 6c. (Before going on with this exercise, stop the progress of time. Go to the menu on the top of the screen, select View, and scroll down to Show Daylight. Set the time at 300x, and the hour and date mentioned below) Now, let s imagine that you are planning a voyage of the Hokule'a, with the legs used in exercises 1 and 5. The journey will commence at 7:30 PM on Friday, September 5 th, 2003 Knowing that each star can be used up to 30 degrees above the horizon, and that the stars rise and set by 1 every 4 minutes, each star can only be used for a maximum of 120 minutes. For each leg of the journey, look toward the rising stars (East) and list the stars that you could use to navigate this course. Also, list the time period for which you can use each star. Are there any time periods when you can't find one of the bright rising stars to use? If so, indicate those times (to the nearest minute). For this part, it will be useful if you change the time interval to seconds. Note that during daylight hours, you will not be able to use the stars and will have to use alternate navigation methods. 5

6 Leg Star/Constellation Time A. B. C. D. E. 7. Other than the celestial bodies (stars, moon, sun, etc.), list 3 aspects of your surroundings that could be used to determine your position and bearing while at sea (this information comes from the online reading). IV. Summary Questions 8. List 2 potential problems or sources of error that one might incur with each navigational system 9. If you were stuck in the middle of the Pacific, and had to get home as soon as possbile, which navigational system would you prefer to use? Why? 6